Electronic sensors are well known in the art for sensing various physical conditions and reporting on the same. By way of example but not limitation, electronic sensors have been developed for sensing temperature, pressure, flow, strain, voltage, current, pH, gases, vibration, light, humidity, motion and the like.
The typical electronic sensor is generally constructed so as to provide a low-level, un-calibrated analog output. In most situations, the output of the electronic sensor must generally be used by a digital controller which is in turn connected to various digital computer control equipment. Thus, it is generally necessary to provide an interface between the electronic sensor and the digital controller so as to properly transform the electronic sensor's analog output signal into a corresponding digital signal which may then be used as an input for the digital controller.
More particularly, FIG. 1 shows a typical prior art construction for connecting the output of an electronic sensor 5 to a digital controller 10. The low-level, un-calibrated analog output of digital sensor 5 is first passed to a signal conditioner 15, where the analog output signal is amplified to a more robust, and hence usable, level. Next, this amplified analog signal is passed to an analog-to-digital converter (or "ADC") 20, where the analog signal is converted into a corresponding digital signal. Finally, this digital signal is passed to digital controller 10, which is in turn connected to digital computer control equipment 25. In this way, the analog output signal generated by electronic sensor 5 may be monitored by digital computer control equipment 25.
Many different types of electronic sensors 5, and many different types of digital controllers 10, are currently available on the market. Thus, with the sort of construction shown in FIG. 1, the user must generally specify, purchase and calibrate the specific signal conditioner 15, and the specific ADC 20, which will be used to convert the low-level, un-calibrated analog output signal provided by electronic sensor 5 into the sort of digital input signal usable by digital controller 10. This process of specification, purchase and calibration generally involves significant time and expense.
In addition to the foregoing, since each independent (or "stand-alone") component in an electronic system is generally characterized by a limited degree of accuracy, the need to position multiple independent components between electronic sensor 5 and digital controller 10 tends to undermine the overall accuracy of the sensor data being reported to digital controller 10. In other words, if a specific stand-alone signal conditioner 15 has an error range of + or -2%, and a specific stand-alone ADC 20 has an error range of + or -2%, a signal passing through those two stand-alone elements will have an error range of + or -4%. Furthermore, since wiring and/or other electrical connectors must generally be used to electrically interconnect stand-alone signal conditioner 15 and stand-alone ADC 20 between electronic sensor 5 and digital controller 10, still other inaccuracies may be introduced into the overall system through the use of stand-alone signal conditioners and stand-alone ADC's.
Currently, digital controller 10 might comprise a so-called "custom" controller, or it might comprise a so-called programmable logic control (or "PLC"), or it might comprise a so-called "micro-PLC". Some custom controllers and some PLC's are constructed so as to incorporate a dedicated ADC directly into the digital controller, whereby the digital controller can accept direct analog inputs. However, other custom controllers, other PLC's, and all of the micro-PLC's currently available on the market are constructed so that they do not incorporate a stand-alone ADC directly into the digital controller. In this situation, the digital controller cannot accept direct analog inputs, and a construction similar to that shown in FIG. 1 must generally be used to connect electronic sensor 5 to digital controller 10.
The present invention is directed to this latter situation, and particularly (but not exclusively) to the situation where digital controller 10 comprises a micro-PLC device.
A further consideration for the present invention relates to the fact that many electronic sensors must necessarily be deployed in harsh and/or hazardous environments. As a result, many of these electronic sensors must periodically be replaced with new electronic sensors. Such sensor replacement typically requires that the old electronic sensor be disconnected from the remainder of the system, the new electronic sensor connected up, and then the new electronic sensor properly calibrated with the remainder of the system. Unfortunately, this replacement process can be inconvenient and time-consuming with system constructions such as that shown in FIG. 1.